The Reactive Extensions for javascript (RxJS) is a set of libraries for composing asynchronous and event-based programs using observable sequences and fluent query operators that many of you already know by Array#extras in javascript. Using RxJS, developers represent asynchronous data streams with Observables, query asynchronous data streams using our many operators, and parameterize the concurrency in the asynchronous data streams using Schedulers. Simply put, RxJS = Observables + Operators + Schedulers.